Opposite Heiligenstadt underground station, the huge red fortress was inaugurated in 1930 by the Austro-Marxist town council that ran Vienna from 1919 to 1934. This monumental structure, designed by Karl Ehn and known to architectural students worldwide, boasts some 1 400 housing units; at the time, there were also shops, laundries, children's play gardens, an infirmary and a library.